The United States strongly rejected Crimea's vote Sunday on breaking away from Ukraine, hinting at possible additional sanctions on Russia.
In a telephone call, US President Barack Obama told his Russian counterpart Vladimir Putin that the vote that found 95.5 percent of ballots in favor of the Crimean Peninsula leaving Ukraine to rejoin Russia violated the Ukrainian constitution.
“President Obama emphasized that the Crimean 'referendum,' which violates the Ukrainian constitution and occurred under duress of Russian military intervention, would never be recognized by the United States and the international community,'' the White House said in a statement.
The vote would mark the most radical redrawing of the map of Europe since Kosovo's 2008 declaration of independence from Serbia.
Joining international condemnation from other world capitals, Obama warned “Russia's actions were in violation of Ukraine's sovereignty and territorial integrity and that, in coordination with our European partners, we are prepared to impose additional costs on Russia for its actions.''
The Kremlin said earlier that the call was initiated by the American side, as relations between Russia and the United States have plunged to their lowest point since the Cold War.
Putin told Obama that the referendum was fully legal, “in line with the norms of international law and the UN charter.''
Ukraine's new pro-European leaders and the West have branded the referendum “illegal'' because the strategic Black Sea region has been under de facto control of Russian forces since the start of the month.
White House spokesman Jay Carney earlier said that Russia had spurned outreach to Ukraine and calls for international monitoring, instead escalating its military intervention into Crimea and initiating military exercises on Ukraine's eastern border.
He called Russia's actions “dangerous and destabilizing.''
Obama stressed that the crisis could still be solved diplomatically, but not so long as “Russian military forces continue their incursions into Ukrainian territory'' and conduct large-scale military exercises along the border with Ukraine, according to the White House.
Russia should support the “immediate'' deployment of international monitors to “help prevent acts of violence by any groups,'' it added.